android - How can I specify the type of the field that an Annotation should be applied to in Java? -


i'm creating simple annotation, me inflating settings inside android application. annotation this:

@target(elementtype.field) @retention(retentionpolicy.runtime) public @interface coresettings {     string name() default ""; }

i want ensure used in fields type extends custom class named basesettings. in example below, mainsettings extends abstract class basesettings.

public class mainactivity extends baseactivity {      @coresettings("prefs")     mainsettings settings;       (...)  }

how can it?

yes, can cause compiler issue error message if write annotation on field of wrong type.

you cannot using @target meta-annotation. in addition, need write annotation processor. annotation processor examine each occurrence of annotation @coresettings in source code, , issues error (just other compiler error) if @coresettings applied type not extend basesettings. short, simple annotation processor write.

you compile-time warning when running annotation processor, can add -processor ... command-line argument javac in project's buildfile.


Comments

Post a Comment

Popular posts from this blog

javascript - Google App Script ContentService downloadAsFile not working -

i have web app developed using google app script htmlservice , html form, populating excel sheet in google drive using spreadsheetapp . , 1 section calling contentservice download data excel file. function doget(e) { // read excel sheet //getappfile(); // render application html template return htmlservice.createtemplatefromfile('index').evaluate() .settitle('go smart') .setsandboxmode(htmlservice.sandboxmode.iframe); } function downloaddoublequatecsvfile() { var sheetid = propertiesservice.getscriptproperties().getproperty('sheetid'); var ss = spreadsheetapp.openbyid(sheetid).getactivesheet(); //var ss = spreadsheetapp.getactivespreadsheet().getactivesheet(); var maxcolumn = ss.getlastcolumn(); var maxrow = ss.getlastrow(); var data = ss.getrange(1, 1, maxrow, maxcolumn).getvalues(); if (data.length > 1) { var csv = ""; (var row = 0; row < data.length; row++) { (var c...
Read more

javascript - Function overwritting -

is there way overwrite function or event handling in function? using addeventlistener, can have many event handlers on element want var test=document.getelementbyid("div"); test.addeventlistener("click",function(){alert("im first");},false); test.addeventlistener("click",function(){alert("im second");},false); // alerts "im first" , after "im second" but if want overwrite function/event example based on client width example this function one() { alert("first"); } function two() { alert("second"); } window.onresize = function() { var test = document.getelementbyid("div"); if (window.innerwidth > 500) { test.onclick = 1 } else { test.onclick = two; } } is possible in javascript? in case use effective little known approach. addeventlistener can accept object property handleevent event handler. in case it's easy overwr...
Read more

c# - Exception when attempting to modify Dictionary -

i creating dictionary manage threads , ran exception when attempt clear dead threads after adding threads dictionary. using system; using system.collections.generic; using system.threading; namespace syscat { public class threadmanager { public static readonly threadmanager globalthreadmanager = new threadmanager( ); /// <summary> /// initializes new instance of <see cref="syscat.threadmanager"/> class. /// </summary> public threadmanager( ) { } /// <summary> /// create new threadmanager threads within basetm , deinitializes basetm /// </summary> public threadmanager( threadmanager basetm ) { this.threads = basetm.threads; basetm.threads.clear( ); } private dictionary<guid,thread> threads = new dictionary<guid, thread>( ); /// <summary> /// attempts obtain unused threadid within ...
Read more